Section D

Factors and Processes that Affect Waste Disposal and Subsurface Transport
of Contaminants in Arid Environments

In 1976, the U.S. Geological Survey (USGS) began studies of unsaturated-zone
hydrology in the Amargosa Desert, near Beatty, Nevada. At that time, the research
was conducted under the auspices of the USGS Low-Level Radioactive Waste Program.
In 1983, agreements with the Bureau of Land Management and the State of Nevada
established two field study areas for sustained study of arid-site processes:
a 16-hectare (ha) area adjacent to a waste-burial facility and a 0.1-ha area
about 3 kilometers farther south. The study areas are collectively known as
the Amargosa Desert Research Site (ADRS). Investigations at the ADRS have
produced long-term benchmark data on hydraulic characteristics and soil-water
movement for undisturbed conditions and for simulated waste-disposal conditions
in arid environments. In 1995, after the unexpected discovery of high concentrations
of tritium and carbon-14 in the unsaturated zone beneath the ADRS, the scope
of research was broadened to include the study of processes affecting radionuclide
transport. The ADRS was incorporated into the USGS Toxic Substances Hydrology
Program in 1997.

The goal of present research at the ADRS is improved understanding of processes
controlling the migration and fate of contaminants in arid environments. Research
at the site is a multidisciplinary collaboration among scientists from universities,
research institutes, national laboratories, and the USGS. The papers that
follow illustrate the main avenues of active research. They explore the application
of new and emerging methods for characterizing hydrogeologic frameworks in
desert alluvial basins; quantifying the exchanges of materials and energy
across the land surface; and understanding the distribution, movement, and
fate of radionuclides in deep unsaturated zones.

Information on ongoing research activities at the Amargosa Desert Research
Site is available on the World Wide Web at: http://nevada.usgs.gov/adrs/.